[igt-dev] [PATCH RFC i-g-t] tests/kms_chamelium: disable output when resetting state

[Daniel Vetter]

On Thu, Jul 11, 2019 at 1:11 PM Simon Ser <simon.ser at intel.com> wrote:
>
> Quoting Imre from the bug comments:
>
> > If unplugging a DP-alt display while there is an active modeset on it, and
> > then replugging the DP-alt display, the HW/FW/driver won't signal the
> > corresponding plug-in hotplug event until the mode is disabled.
> >
> > The failing tests do this:
> >
> > - <have the output enabled>
> > - unplug the display, keeping the output enabled
> > - wait/poll for the disconnect status -> success
> > - replug the display, while the output is still enabled
> > - wait/poll for the connect status -> fail
> >
> > This sequence is not supported with DP-alt sinks (like the USB-C to HDMI
> > dongle), as I described above.
>
> This patch changes reset_state to disable the output before unplugging the
> connector (via chamelium_reset).
>
> Signed-off-by: Simon Ser <simon.ser at intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111045
> ---
>
> This is just a RFC to check that the root issue is what we think it is.

Yeah we can't merge this, this would completely break the hotunplug
usecase, which is:
1. user yanks cable
2. desktop reacts to hotunplug and shuts down the screen

If the hw can't do a hotunplug while there's an active mode, then we
have a chicken&egg situation, and we need to resort to some form of
polling (hooray). Hotunplug better work if the display is on.

Historical aside: Polling is disabled on may old VGA outputs because
the polling can result in screen flickering/corruption. But hw got
better, so even VGA managed to handle hotunplug correctly. No DE (or
user fwiw) assumes nowadays that hotunplug is broken.
-Daniel

>  tests/kms_chamelium.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/tests/kms_chamelium.c b/tests/kms_chamelium.c
> index b749b5598c1d..f538ad394480 100644
> --- a/tests/kms_chamelium.c
> +++ b/tests/kms_chamelium.c
> @@ -216,6 +216,13 @@ static void
>  reset_state(data_t *data, struct chamelium_port *port)
>  {
>         int p;
> +       drmModeConnector *connector;
> +       igt_output_t *output;
> +
> +       connector = chamelium_port_get_connector(data->chamelium, port, false);
> +       output = igt_output_from_connector(&data->display, connector);
> +       igt_output_set_pipe(output, PIPE_NONE);
> +       igt_display_commit2(&data->display, COMMIT_ATOMIC);
>
>         chamelium_reset(data->chamelium);
>
> --
> 2.22.0
>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch